<!DOCTYPE HTML>
<html lang="zh-CN">


<head>
    <meta charset="utf-8">
    <meta name="keywords" content="《java并发编程的艺术》第六章总结1, 戴某的博客">
    <meta name="description" content="戴某的笔记">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=no">
    <meta name="renderer" content="webkit|ie-stand|ie-comp">
    <meta name="mobile-web-app-capable" content="yes">
    <meta name="format-detection" content="telephone=no">
    <meta name="apple-mobile-web-app-capable" content="yes">
    <meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">
    <!-- Global site tag (gtag.js) - Google Analytics -->


    <title>《java并发编程的艺术》第六章总结1 | 戴某的博客</title>
    <link rel="icon" type="image/png" href="/dai_modest/favicon.png">

    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/awesome/css/all.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/materialize/materialize.min.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/aos/aos.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/animate/animate.min.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/lightGallery/css/lightgallery.min.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/css/matery.css">
    <link rel="stylesheet" type="text/css" href="/dai_modest/css/my.css">

    <script src="/dai_modest/libs/jquery/jquery.min.js"></script>

<meta name="generator" content="Hexo 5.4.0"><link rel="alternate" href="/dai_modest/atom.xml" title="戴某的博客" type="application/atom+xml">
<link rel="stylesheet" href="/dai_modest/css/prism-tomorrow.css" type="text/css"></head>



   <style>
    body{
       background-image: url(https://cdn.jsdelivr.net/gh/Tokisaki-Galaxy/res/site/medias/background.jpg);
       background-repeat:no-repeat;
       background-size:cover;
       background-attachment:fixed;
    }
</style>



<body>
    <header class="navbar-fixed">
    <nav id="headNav" class="bg-color nav-transparent">
        <div id="navContainer" class="nav-wrapper container">
            <div class="brand-logo">
                <a href="/dai_modest/" class="waves-effect waves-light">
                    
                    <img src="/dai_modest/medias/logo.png" class="logo-img" alt="LOGO">
                    
                    <span class="logo-span">戴某的博客</span>
                </a>
            </div>
            

<a href="#" data-target="mobile-nav" class="sidenav-trigger button-collapse"><i class="fas fa-bars"></i></a>
<ul class="right nav-menu">
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/" class="waves-effect waves-light">
      
      <i class="fas fa-home" style="zoom: 0.6;"></i>
      
      <span>首页</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/tags" class="waves-effect waves-light">
      
      <i class="fas fa-tags" style="zoom: 0.6;"></i>
      
      <span>标签</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/categories" class="waves-effect waves-light">
      
      <i class="fas fa-bookmark" style="zoom: 0.6;"></i>
      
      <span>分类</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/archives" class="waves-effect waves-light">
      
      <i class="fas fa-archive" style="zoom: 0.6;"></i>
      
      <span>归档</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/about" class="waves-effect waves-light">
      
      <i class="fas fa-user-circle" style="zoom: 0.6;"></i>
      
      <span>关于</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/contact" class="waves-effect waves-light">
      
      <i class="fas fa-comments" style="zoom: 0.6;"></i>
      
      <span>留言板</span>
    </a>
    
  </li>
  
  <li class="hide-on-med-and-down nav-item">
    
    <a href="/dai_modest/friends" class="waves-effect waves-light">
      
      <i class="fas fa-address-book" style="zoom: 0.6;"></i>
      
      <span>友情链接</span>
    </a>
    
  </li>
  
  <li>
    <a href="#searchModal" class="modal-trigger waves-effect waves-light">
      <i id="searchIcon" class="fas fa-search" title="搜索" style="zoom: 0.85;"></i>
    </a>
  </li>
</ul>


<div id="mobile-nav" class="side-nav sidenav">

    <div class="mobile-head bg-color">
        
        <img src="/dai_modest/medias/logo.png" class="logo-img circle responsive-img">
        
        <div class="logo-name">戴某的博客</div>
        <div class="logo-desc">
            
            戴某的笔记
            
        </div>
    </div>

    

    <ul class="menu-list mobile-menu-list">
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-home"></i>
			
			首页
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/tags" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-tags"></i>
			
			标签
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/categories" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-bookmark"></i>
			
			分类
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/archives" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-archive"></i>
			
			归档
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/about" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-user-circle"></i>
			
			关于
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/contact" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-comments"></i>
			
			留言板
		</a>
          
        </li>
        
        <li class="m-nav-item">
	  
		<a href="/dai_modest/friends" class="waves-effect waves-light">
			
			    <i class="fa-fw fas fa-address-book"></i>
			
			友情链接
		</a>
          
        </li>
        
        
        <li><div class="divider"></div></li>
        <li>
            <a href="https://github.com/blinkfox/hexo-theme-matery" class="waves-effect waves-light" target="_blank">
                <i class="fab fa-github-square fa-fw"></i>Fork Me
            </a>
        </li>
        
    </ul>
</div>


        </div>

        
            <style>
    .nav-transparent .github-corner {
        display: none !important;
    }

    .github-corner {
        position: absolute;
        z-index: 10;
        top: 0;
        right: 0;
        border: 0;
        transform: scale(1.1);
    }

    .github-corner svg {
        color: #0f9d58;
        fill: #fff;
        height: 64px;
        width: 64px;
    }

    .github-corner:hover .octo-arm {
        animation: a 0.56s ease-in-out;
    }

    .github-corner .octo-arm {
        animation: none;
    }

    @keyframes a {
        0%,
        to {
            transform: rotate(0);
        }
        20%,
        60% {
            transform: rotate(-25deg);
        }
        40%,
        80% {
            transform: rotate(10deg);
        }
    }
</style>

<a href="https://github.com/blinkfox/hexo-theme-matery" class="github-corner tooltipped hide-on-med-and-down" target="_blank"
   data-tooltip="Fork Me" data-position="left" data-delay="50">
    <svg viewBox="0 0 250 250" aria-hidden="true">
        <path d="M0,0 L115,115 L130,115 L142,142 L250,250 L250,0 Z"></path>
        <path d="M128.3,109.0 C113.8,99.7 119.0,89.6 119.0,89.6 C122.0,82.7 120.5,78.6 120.5,78.6 C119.2,72.0 123.4,76.3 123.4,76.3 C127.3,80.9 125.5,87.3 125.5,87.3 C122.9,97.6 130.6,101.9 134.4,103.2"
              fill="currentColor" style="transform-origin: 130px 106px;" class="octo-arm"></path>
        <path d="M115.0,115.0 C114.9,115.1 118.7,116.5 119.8,115.4 L133.7,101.6 C136.9,99.2 139.9,98.4 142.2,98.6 C133.8,88.0 127.5,74.4 143.8,58.0 C148.5,53.4 154.0,51.2 159.7,51.0 C160.3,49.4 163.2,43.6 171.4,40.1 C171.4,40.1 176.1,42.5 178.8,56.2 C183.1,58.6 187.2,61.8 190.9,65.4 C194.5,69.0 197.7,73.2 200.1,77.6 C213.8,80.2 216.3,84.9 216.3,84.9 C212.7,93.1 206.9,96.0 205.4,96.6 C205.1,102.4 203.0,107.8 198.3,112.5 C181.9,128.9 168.3,122.5 157.7,114.1 C157.9,116.9 156.7,120.9 152.7,124.9 L141.0,136.5 C139.8,137.7 141.6,141.9 141.8,141.8 Z"
              fill="currentColor" class="octo-body"></path>
    </svg>
</a>
        
    </nav>

</header>

    



<div class="bg-cover pd-header post-cover" style="background-image: url('/dai_modest/medias/featureimages/8.jpg')">
    <div class="container" style="right: 0px;left: 0px;">
        <div class="row">
            <div class="col s12 m12 l12">
                <div class="brand">
                    <h1 class="description center-align post-title">《java并发编程的艺术》第六章总结1</h1>
                </div>
            </div>
        </div>
    </div>
</div>




<main class="post-container content">

    
    <link rel="stylesheet" href="/dai_modest/libs/tocbot/tocbot.css">
<style>
    #articleContent h1::before,
    #articleContent h2::before,
    #articleContent h3::before,
    #articleContent h4::before,
    #articleContent h5::before,
    #articleContent h6::before {
        display: block;
        content: " ";
        height: 100px;
        margin-top: -100px;
        visibility: hidden;
    }

    #articleContent :focus {
        outline: none;
    }

    .toc-fixed {
        position: fixed;
        top: 64px;
    }

    .toc-widget {
        width: 345px;
        padding-left: 20px;
    }

    .toc-widget .toc-title {
        padding: 35px 0 15px 17px;
        font-size: 1.5rem;
        font-weight: bold;
        line-height: 1.5rem;
    }

    .toc-widget ol {
        padding: 0;
        list-style: none;
    }

    #toc-content {
        padding-bottom: 30px;
        overflow: auto;
    }

    #toc-content ol {
        padding-left: 10px;
    }

    #toc-content ol li {
        padding-left: 10px;
    }

    #toc-content .toc-link:hover {
        color: #42b983;
        font-weight: 700;
        text-decoration: underline;
    }

    #toc-content .toc-link::before {
        background-color: transparent;
        max-height: 25px;

        position: absolute;
        right: 23.5vw;
        display: block;
    }

    #toc-content .is-active-link {
        color: #42b983;
    }

    #floating-toc-btn {
        position: fixed;
        right: 15px;
        bottom: 76px;
        padding-top: 15px;
        margin-bottom: 0;
        z-index: 998;
    }

    #floating-toc-btn .btn-floating {
        width: 48px;
        height: 48px;
    }

    #floating-toc-btn .btn-floating i {
        line-height: 48px;
        font-size: 1.4rem;
    }
</style>
<div class="row">
    <div id="main-content" class="col s12 m12 l9">
        <!-- 文章内容详情 -->
<div id="artDetail">
    <div class="card">
        <div class="card-content article-info">
            <div class="row tag-cate">
                <div class="col s7">
                    
                    <div class="article-tag">
                        
                            <a href="/dai_modest/tags/java/">
                                <span class="chip bg-color">java</span>
                            </a>
                        
                    </div>
                    
                </div>
                <div class="col s5 right-align">
                    
                    <div class="post-cate">
                        <i class="fas fa-bookmark fa-fw icon-category"></i>
                        
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/" class="post-category">
                                书籍
                            </a>
                        
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/" class="post-category">
                                笔记类
                            </a>
                        
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/%E3%80%8Ajava%E5%B9%B6%E5%8F%91%E7%BC%96%E7%A8%8B%E7%9A%84%E8%89%BA%E6%9C%AF%E3%80%8B/" class="post-category">
                                《java并发编程的艺术》
                            </a>
                        
                    </div>
                    
                </div>
            </div>

            <div class="post-info">
                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-minus fa-fw"></i>发布日期:&nbsp;&nbsp;
                    2022-04-16
                </div>
                

                
                <div class="post-date info-break-policy">
                    <i class="far fa-calendar-check fa-fw"></i>更新日期:&nbsp;&nbsp;
                    2022-05-21
                </div>
                

                
                <div class="info-break-policy">
                    <i class="far fa-file-word fa-fw"></i>文章字数:&nbsp;&nbsp;
                    4k
                </div>
                

                

                
            </div>
        </div>
        <hr class="clearfix">

        
        <!-- 是否加载使用自带的 prismjs. -->
        <link rel="stylesheet" href="/dai_modest/libs/prism/prism.css">
        

        
        <!-- 代码块折行 -->
        <style type="text/css">
            code[class*="language-"], pre[class*="language-"] { white-space: pre-wrap !important; }
        </style>
        

        <div class="card-content article-card-content">
            <div id="articleContent">
                <h1 id="ConcurrentHashMap"><a href="#ConcurrentHashMap" class="headerlink" title="ConcurrentHashMap"></a>ConcurrentHashMap</h1><p>在并发编程中使用HashMap可能会导致程序死循环，而使用线程安全的HashTable效率又非常低下，这时候就出现了效率高且线程安全的ConcurrentHashMap。</p>
<h2 id="多线程的HashMap的put操作出现死循环"><a href="#多线程的HashMap的put操作出现死循环" class="headerlink" title="多线程的HashMap的put操作出现死循环"></a>多线程的HashMap的put操作出现死循环</h2><p>主要情况：</p>
<p>1.多线程put操作后，get操作导致死循环。</p>
<p>2.多线程put非null元素后，get操作得到null值。</p>
<p>3.多线程put操作，导致元素丢失。</p>
<p>HashMap是采用链表解决Hash冲突，因为是链表结构，那么就很容易形成闭合的链路，这样在循环的时候只要有线程对这个HashMap进行get操作操作就会产生死循环。</p>
<p>扩容源码</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">void transfer(Entry[] newTable)
&#123;
 Entry[] src &#x3D; table;
 int newCapacity &#x3D; newTable.length;
 &#x2F;&#x2F;下面这段代码的意思是：
 &#x2F;&#x2F;  从OldTable里摘一个元素出来，然后放到NewTable中
 for (int j &#x3D; 0; j &lt; src.length; j++) &#123;
  Entry&lt;K,V&gt; e &#x3D; src[j];
  if (e !&#x3D; null) &#123;
   src[j] &#x3D; null;
   do &#123;
    Entry&lt;K,V&gt; next &#x3D; e.next;&#x2F;&#x2F;取出第一个元素
    int i &#x3D; indexFor(e.hash, newCapacity);
    e.next &#x3D; newTable[i];
    newTable[i] &#x3D; e;
    e &#x3D; next;
   &#125; while (e !&#x3D; null);
  &#125;
 &#125;
&#125;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<p>如果两个线程同时执行put并需要扩容 这时候就会出现死循环。</p>
<p><strong>初始的Hashmap</strong></p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/%E5%88%9D%E5%A7%8Bhashmap.png" alt="image-20220521104101721"></p>
<p><strong>1.当线程1，线程2同时执行但是线程1因为某些情况暂停执行。</strong></p>
<p>出现下面情况：</p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/hashmap%E5%A4%9A%E7%BA%BF%E7%A8%8B%E6%89%A9%E5%AE%B91.png" alt="image-20220521103835018"></p>
<p><strong>2.但是这时候线程1被调度回来继续执行刚刚的put和扩容操作，并重新执行了newTable[i]=e 重新创建了一个数组，并开始存元素。</strong></p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/hashmap%E5%A4%9A%E7%BA%BF%E7%A8%8B%E6%89%A9%E5%AE%B92.png" alt="image-20220521104314273"></p>
<p><img src="C:\Users\86179\AppData\Roaming\Typora\typora-user-images\image-20220521111746256.png" alt="image-20220521111746256"></p>
<p>3.开始了新的一轮while循环，执行Entry&lt;K,V&gt;next=e.next;因为线程2已经将key(7)的next指向了key(3),所以next=key(3)。</p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/hashmap%E5%A4%9A%E7%BA%BF%E7%A8%8B%E6%89%A9%E5%AE%B94.png" alt="image-20220521112126388"></p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/hashmap%E5%A4%9A%E7%BA%BF%E7%A8%8B%E6%89%A9%E5%AE%B95.png" alt="image-20220521112908633"></p>
<p>这样key3和key7形成了循环列表。</p>
<h2 id="扩容出现死循环总结"><a href="#扩容出现死循环总结" class="headerlink" title="扩容出现死循环总结"></a>扩容出现死循环总结</h2><p>HashMap之所以在并发下的扩容造成死循环，是因为，<strong>多个线程并发进行时，因为一个线程先期完成了扩容，将原的链表重新散列到自己的表中，并且链表变成了倒序，后一个线程再扩容时，又进行自己的散列，再次将倒序链表变为正序链表</strong>。于是形成了一个环形链表，当表中不存在的元素时，造成死循环。</p>
<p>视频连接：<a target="_blank" rel="noopener" href="https://www.bilibili.com/video/BV1eU4y1m79W?p=8">https://www.bilibili.com/video/BV1eU4y1m79W?p=8</a></p>
<p>但是在JDK1.8中开发小组修复了这种问题。但是hashmap还是有很多并发问题。</p>
<h2 id="HashTable和ConcurrentHashMap的效率"><a href="#HashTable和ConcurrentHashMap的效率" class="headerlink" title="HashTable和ConcurrentHashMap的效率"></a>HashTable和ConcurrentHashMap的效率</h2><p>HashTable容器使用synchronize来保证线程安全，但是效率低下，因为当一个线程访问HashTable的同步方法，其他线程也访问HashTable的同步方法时，会进入阻塞或轮询状态。所以当竞争越来越激烈的情况下，竞争同一把锁的的情况越明显那么效率就会越来越低下。</p>
<p>ConcurrentHashMap使用了锁分段技术可以有效提升并发访问量，锁分段技术就是解决想HashTable这种多种竞争同一把锁的情况，<strong>容器中有多把锁，每一把锁用于锁定锁容器一部分数据而不是全部数据</strong>，那么当多线程访问容器里不同数据段的数据时，线程就不会存在锁竞争，从而有效提高并发访问效率。</p>
<p><strong>核心：首先将数据分成一段一段地存储，然后给每一段数据配一把锁，当一个线程占用锁访问其中一个段数据的时候，其他段的数据也能被其他线程访问。</strong></p>
<h1 id="ConcurrentHashMap的结构"><a href="#ConcurrentHashMap的结构" class="headerlink" title="ConcurrentHashMap的结构"></a>ConcurrentHashMap的结构</h1><p>ConcurrentHashMap是由Segment数组结构和HashEntry数组结构组成。Segment是一种可重入锁（ReentrantLock），HashEntry则是用于存储键值对数据。一个ConcurrentHashMap里面包含<strong>一个Segment数组</strong>，Segment的结构和HashMap类似，是一种数组和链表结构。<strong>一个Segment里面包含一个HashEntry数组</strong>，每个HashEntry是一个链表结构的元素。</p>
<p><strong>每个Segment守护着一个HashEntry数组里的元素，当HashEntry数组的数据进行修改时，必须首先获得与它对应的Segment锁。</strong></p>
<p><strong>1.7和1.8的ConcurrentHashMap的异同</strong></p>
<p>相同点：</p>
<p>1.都不允许key和value为null，否则会抛出异常。</p>
<p>2.和HashMap的功能基本一致，重点解决了HashMap多线程的不安全问题。</p>
<p>不同点：</p>
<pre class="line-numbers language-none"><code class="language-none">DK1.7中的ConcurrentHashMap采用了数组+Segment+分段锁的基本设计理念，简单理解就是切分成多个（默认是16）Segment（分段锁）块。Segment继承自ReentrantLock锁，所以并发操作时每个Segment互不影响，理论上是可以支持CurrencyLevel(Segment数组大小)的并发度的。对于每段Segment，保证只有一个线程能够访问，但是与其它段的线程互不冲突，实现了真正的并发访问。<span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>

<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/ConcurrentHashMap%E7%BB%93%E6%9E%841.png" alt="image-20220521115933258"></p>
<pre class="line-numbers language-none"><code class="language-none">JDK1.8中将Segment块换成了Node，每个Node采用循环CAS + synchronized实现线程安全，即每个Node都有自己的并发度。<span aria-hidden="true" class="line-numbers-rows"><span></span></span></code></pre>

<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/ConcurrentHasp1.8%E7%BB%93%E6%9E%84.png" alt="image-20220521120012010"></p>
<pre class="line-numbers language-none"><code class="language-none">出现hash冲突时，1.7中采用采用链表进行存储，而1.8中和HashMap相似，先链表存储，达到阈值再转换为红黑树来优化查询。也因此，链表查询复杂度在1.7中为O(N)，而1.8中红黑树优化为O(logN))。
1.8的锁粒度变小，从对每个Segment段加锁，变为对每个Node节点加锁。
对于1.7中的ConcurrentHashMap，进行哈希操作有两步，效率偏低，因为此时需要先找出Segment段，再在其中寻找对应的桶。<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span></span></code></pre>



<h2 id="ConcurrentHashMap操作（JDK1-7）"><a href="#ConcurrentHashMap操作（JDK1-7）" class="headerlink" title="ConcurrentHashMap操作（JDK1.7）"></a>ConcurrentHashMap操作（JDK1.7）</h2><p>既然ConcurrentHashMap使用分段锁Segment来保护不同段的数据，那么在插入和获取元素的时候，必须先通过散列算法定位到Segment。之所以进行再散列（让每一个位都能参与到散列算法中）是为了减少散列冲突，能够使元素均匀分布在不同的Segment上，从而提高容器的存取效率。</p>
<h3 id="get操作"><a href="#get操作" class="headerlink" title="get操作"></a>get操作</h3><p>先进行一次再散列（hash(key.hashCode)）,然后使用这个散列值通过散列算法定位到哦Segment，再通过散列算法定位到元素。</p>
<p>get高效的原因，整个get过程并没有加锁，除非读到的值是null才会被加锁重读。因为ConcurrentHashMap的get方法中使用的共享变量都定义成volatile类型，如用于统计当前Segment大小的count字段和用于存储值的HashENtry的Value。</p>
<p>所以根据java内存模型中的happen before原则，对volatile字段的写入操作先于读操作，即使两个线程同时修改和获取volatile变量，get操作也能够拿到最新的值。</p>
<h3 id="put操作"><a href="#put操作" class="headerlink" title="put操作"></a>put操作</h3><p>操作共享变量必须加锁，put方法首先定位到Segment，然后在Segment里面进行插入操作；。</p>
<p>1.判断是否需要对Segment里面的HashEntry数组进行扩容。</p>
<p>2.定位添加元素的位置，然后将其放在HashEntry数组里。</p>
<p>如何扩容：在扩容的时候会创建一个容量为原来两倍的数组，然后对原数组里的元素进行再散列后插入到新的数组里。为了高效，ConcurrentHashMap不会对整个容器进行扩容而只对某个segment进行扩容。</p>
<h3 id="size操作"><a href="#size操作" class="headerlink" title="size操作"></a>size操作</h3><p>如果使用加锁的方法再每次计算size方法的时候对其他方法进行加锁，那么效率是十分低下的。ConcurrentHashMap的做法是先尝试2次通过不锁做Segment的方法来统计各个Segment大小，如果统计过程中，容器的count发生了变化，则再采用加锁的方式来统计所有Segment的大小。</p>
<h2 id="ConcurrentHaspMap操作（JDK1-8）"><a href="#ConcurrentHaspMap操作（JDK1-8）" class="headerlink" title="ConcurrentHaspMap操作（JDK1.8）"></a>ConcurrentHaspMap操作（JDK1.8）</h2><p>重要的成员变量</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java">&#x2F;&#x2F; ConcurrentHashMap 的底层结构，默认为 null，懒加载
&#x2F;&#x2F; 初始化发生在第一次 put() 时，默认大小为 16
transient volatile Node&lt;K,V&gt;[] table;

&#x2F;&#x2F; 默认为 null，扩容时新生成的数组，通常其大小为原数组的两倍
private transient volatile Node&lt;K,V&gt;[] nextTable;

&#x2F;&#x2F; 用于数组初始化与扩容控制
private transient volatile int sizeCtl;
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>



<h3 id="sizectl"><a href="#sizectl" class="headerlink" title="sizectl"></a>sizectl</h3><p><strong>当前位初始化时</strong>，sizeCtl=0表示为指定初始熔炼，如果大于0表示由指定容量计算最近的2的n次幂来作为初始容量值。</p>
<p><strong>在初始过程中</strong>，sizeCtl=-1表示table正在初始化，sizeCtl=-N表示有N-1一个线程正在进行扩容操作。</p>
<p><strong>初始完成</strong>，其值为table.length*0.75，表示将扩容阈值调为容量大小的0.75倍。</p>
<h3 id="get-操作"><a href="#get-操作" class="headerlink" title="get()操作"></a>get()操作</h3><pre class="line-numbers language-java" data-language="java"><code class="language-java">public V get(Object key) &#123;
        Node&lt;K,V&gt;[] tab; Node&lt;K,V&gt; e, p; int n, eh; K ek;
        &#x2F;&#x2F; 根据 key 计算出桶的位置
        int h &#x3D; spread(key.hashCode());
        if ((tab &#x3D; table) !&#x3D; null &amp;&amp; (n &#x3D; tab.length) &gt; 0 &amp;&amp;
            (e &#x3D; tabAt(tab, (n - 1) &amp; h)) !&#x3D; null) &#123;
            if ((eh &#x3D; e.hash) &#x3D;&#x3D; h) &#123;
                &#x2F;&#x2F; 就是桶节点，直接返回
                if ((ek &#x3D; e.key) &#x3D;&#x3D; key || (ek !&#x3D; null &amp;&amp; key.equals(ek)))
                    return e.val;
            &#125;
            &#x2F;&#x2F; 树节点，进行红黑树查找
            else if (eh &lt; 0)
                return (p &#x3D; e.find(h, key)) !&#x3D; null ? p.val : null;
            &#x2F;&#x2F; 链表，直接遍历查找
            while ((e &#x3D; e.next) !&#x3D; null) &#123;
                if (e.hash &#x3D;&#x3D; h &amp;&amp;
                    ((ek &#x3D; e.key) &#x3D;&#x3D; key || (ek !&#x3D; null &amp;&amp; key.equals(ek))))
                    return e.val;
            &#125;
        &#125;
        return null;
&#125;<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>





<h3 id="put-操作"><a href="#put-操作" class="headerlink" title="put()操作"></a>put()操作</h3><pre class="line-numbers language-java" data-language="java"><code class="language-java">&#x2F;&#x2F; 当设置为 false 时表示这个 value 一定会设置
public V put(K key, V value) &#123;
        return putVal(key, value, false);
&#125;

final V putVal(K key, V value, boolean onlyIfAbsent) &#123;
		&#x2F;&#x2F; 拒绝 null
        if (key &#x3D;&#x3D; null || value &#x3D;&#x3D; null) throw new NullPointerException();
        &#x2F;&#x2F; 根据 key 计算出 hashcode
        int hash &#x3D; spread(key.hashCode());
        int binCount &#x3D; 0;
        for (Node&lt;K,V&gt;[] tab &#x3D; table;;) &#123;
            Node&lt;K,V&gt; f; int n, i, fh;
            &#x2F;&#x2F; 这是 Map 第一次被使用，需要进行初始化
            if (tab &#x3D;&#x3D; null || (n &#x3D; tab.length) &#x3D;&#x3D; 0)
                &#x2F;&#x2F; CAS 进行数组初始化
                tab &#x3D; initTable();
            &#x2F;&#x2F; 当前 key 通过 (n-1) &amp; hash 定位出的位置如果为空，则表示当前位置可以直接写入数据
            else if ((f &#x3D; tabAt(tab, i &#x3D; (n - 1) &amp; hash)) &#x3D;&#x3D; null) &#123;
            	&#x2F;&#x2F; 利用 CAS 尝试写入，失败则自旋保证成功
            	&#x2F;&#x2F; 此时采用乐观锁，不需要加互斥锁
                if (casTabAt(tab, i, null, new Node&lt;K,V&gt;(hash, key, value, null)))
                    break;                   
            &#125;
            &#x2F;&#x2F; 如果当前桶的头节点的 hash 为 MOVED，那么当前 Map 正在扩容，则当前线程先协助扩容，再更新值
            else if ((fh &#x3D; f.hash) &#x3D;&#x3D; MOVED)
                tab &#x3D; helpTransfer(tab, f);
            &#x2F;&#x2F; 出现了 Hash 冲突，数组也没在扩容，开始遍历链表进行插值
            else &#123;
                V oldVal &#x3D; null;
                &#x2F;&#x2F; 加重量级锁，再进行插入
                synchronized (f) &#123;
                    &#x2F;&#x2F; 再次计算出要存储的位置的桶元素，跟前面取出来的比较
                    if (tabAt(tab, i) &#x3D;&#x3D; f) &#123;
                        &#x2F;&#x2F; 是链表节点，开始遍历
                        &#x2F;&#x2F; 当转换为树之后，hash 为 -2
                        if (fh &gt;&#x3D; 0) &#123;
                            &#x2F;&#x2F; 节点计数
                            binCount &#x3D; 1;
                            for (Node&lt;K,V&gt; e &#x3D; f;; ++binCount) &#123;
                                K ek;
                                &#x2F;&#x2F; 要存的元素的 hash 与 key 跟要存储的位置的相同时，替换掉该节点的 value
                                if (e.hash &#x3D;&#x3D; hash &amp;&amp;
                                    ((ek &#x3D; e.key) &#x3D;&#x3D; key ||
                                     (ek !&#x3D; null &amp;&amp; key.equals(ek)))) &#123;
                                    oldVal &#x3D; e.val;
                                    &#x2F;&#x2F; 当使用的是 putIfAbsent() 时，只有在这个 key 没有设置值时才进行 value 设置
                                    if (!onlyIfAbsent)
                                        e.val &#x3D; value;
                                    break;
                                &#125;
                                Node&lt;K,V&gt; pred &#x3D; e;
                                &#x2F;&#x2F; 如果没有找到同样的 hash 和 key，则判断该节点的下一个节点是否为空
                                if ((e &#x3D; e.next) &#x3D;&#x3D; null) &#123;
                                    &#x2F;&#x2F; 直接尾插
                                    pred.next &#x3D; new Node&lt;K,V&gt;(hash, key, value, null);
                                    break;
                                &#125;
                            &#125;
                        &#125;
                        &#x2F;&#x2F; 已转为红黑树节点
                        else if (f instanceof TreeBin) &#123;
                            Node&lt;K,V&gt; p;
                            binCount &#x3D; 2;
                            &#x2F;&#x2F; 调用 putTreeVal()，执行红黑树逻辑，将该元素添加到树中去
                            if ((p &#x3D; ((TreeBin&lt;K,V&gt;)f).putTreeVal(hash, key, value)) !&#x3D; null) &#123;
                                oldVal &#x3D; p.val;
                                if (!onlyIfAbsent)
                                    p.val &#x3D; value;
                            &#125;
                        &#125;
                    &#125;
                &#125;
                if (binCount !&#x3D; 0) &#123;
                    &#x2F;&#x2F; 当在同一个桶的节点数目达到 8 时，进行链表转红黑树操作
                    if (binCount &gt;&#x3D; TREEIFY_THRESHOLD)
                        treeifyBin(tab, i);
                    if (oldVal !&#x3D; null)
                        return oldVal;
                    break;
                &#125;
            &#125;
        &#125;
        &#x2F;&#x2F; 计数，是否扩容判定
        addCount(1L, binCount);
        return null;
&#125;
<span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>总结：</p>
<p>1.先进性null判断。</p>
<p>2.然后进行数组的初始化判断，如果为null，则调用initTable()进行CAS操作，初始数组。</p>
<p>3.如果节点要放入的桶为空，则直接将该节点插入，利用CAS，而不用加互斥锁。</p>
<p>4.如果hash对应铜的节点hash为MOVED，则说明正在发送扩容，当前线程直接调用helpTransfer()帮忙扩容，再进行插值。</p>
<p>5.如果这个节点，不为空，也不在扩容，则通过synchronized来加锁，进行添加操作。</p>
<p>6.如果当前桶中的是链表，则进行链表遍历，要么覆盖值，要么尾插。</p>
<p>7.如果是树节点，则执行putTreeVal()，往红黑树中插值。</p>
<p>8.最后进行判断，如果桶中节点达到8个，调用treeBin()进行链表转树操作。</p>
<p>9.最后调用addCount()进行计数，判断是否需要扩容。</p>
<h3 id="treeifyBin"><a href="#treeifyBin" class="headerlink" title="treeifyBin()"></a>treeifyBin()</h3><p>逻辑和HashMap中相似，如果数组长度小于64，则调用tryPresize()扩张数组长度一倍，否则把链表转为树。</p>
<p>在tryPresize方法中没有加锁，允许多个线程进入，扩容及节点迁移过程中调用transfer(),如果数组正在扩张，进行节点迁移，则当前线程也需要帮助扩容，一般情况下，扩容也是两倍。</p>
<h3 id="transfer-（扩容核心）"><a href="#transfer-（扩容核心）" class="headerlink" title="transfer()（扩容核心）"></a>transfer()（扩容核心）</h3><p>扩容核心，当table的元素数量达到阈值sizeCtl，需要对table进行扩容，同时把数组中的节点复制到新的数组的相同位置。主要是两步：1.构建一个nextTable，大小为table两倍；2.把table的数据复制到nextTable中。只有treePresize、helpTransfer和addCount三个方法会调用它。</p>
<p>在扩容过程中，依然支持并发复制及插入。</p>
<h1 id="ConcurrentLinkedQueue"><a href="#ConcurrentLinkedQueue" class="headerlink" title="ConcurrentLinkedQueue"></a>ConcurrentLinkedQueue</h1><p>在并发编程中，有时候需要使用线程安全的队列，如果要实现一个线程安全的队列有两种方式：一种是使用阻塞算法，另一种是使用非阻塞算法。</p>
<p>阻塞算法的队列可以用一个锁（出队入队一把锁）或两个锁（出队入队两把锁）等方式来实现。非阻塞实现方式可以使用循环CAS方式来实现。</p>
<p>ConcurrentLinkedQueue是一个基于链接节点的无界安全队列，它采用先进先出的规则对节点进行排序。本身是由head节点和tail节点组成，每个节点由节点元素（item）和指向下一个节点（next）的引用组成，默认情况下head节点存储的元素为空。</p>
<p><img src="https://gitee.com/modest2001/img/raw/master/yygh/ConcurrentLinkedQueue%E5%9B%BE%E8%A7%A3.png" alt="image-20220521132030799"></p>
<p><strong>定位尾节点</strong>：tail节点并不总是尾节点，所以每次入队都必须先通过tail节点来找到尾节点。如果tail及诶点的next节点不为空，则将入队节点设置为tail节点，如果tail节点的next节点为空，则将入队节点设置成tail的next节点，所以tail节点不总为尾节点。</p>
<p><strong>出队列</strong>：当head节点里面有元素时，直接弹出head节点里的元素，而不会更新head节点。只有当head节点里没有元素时，出队操作才会更新head节点。（使用CAS操作判断头节点是否为null，在进行操作）</p>
<p><strong>HOPS的设置意图</strong></p>
<p>为了解决吗每次都需要使用循环CAS更新tail节点，如果能减少CAS更新tail节点的次数，就能够提高入队的效率，所以doug lea使用hops变量来控制并减少tail节点的更新频率。</p>
<p>当tail和尾节点的距离大于等于HOPS的值（默认为1）时才会更新tail节点，tail节点和尾节点的距离越长，使用CAS更新tail节点的次数就会越少。</p>
<p>本质上来说：它是通过增加对volatile变量的读操作来减少对volatile变量的写操作，而对volatile变量的写操作开销要远远大于读操作，如果入队效率会有所提升。</p>

                
            </div>
            <hr/>

            

    <div class="reprint" id="reprint-statement">
        
            <div class="reprint__author">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-user">
                        文章作者:
                    </i>
                </span>
                <span class="reprint-info">
                    <a href="/dai_modest/about" rel="external nofollow noreferrer">戴某人</a>
                </span>
            </div>
            <div class="reprint__type">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-link">
                        文章链接:
                    </i>
                </span>
                <span class="reprint-info">
                    <a href="https://modest2001.gitee.io/dai_modest/dai_modest/2022/04/16/java-bing-fa-bian-cheng-de-yi-zhu-di-liu-zhang-zong-jie-1/">https://modest2001.gitee.io/dai_modest/dai_modest/2022/04/16/java-bing-fa-bian-cheng-de-yi-zhu-di-liu-zhang-zong-jie-1/</a>
                </span>
            </div>
            <div class="reprint__notice">
                <span class="reprint-meta" style="font-weight: bold;">
                    <i class="fas fa-copyright">
                        版权声明:
                    </i>
                </span>
                <span class="reprint-info">
                    本博客所有文章除特別声明外，均采用
                    <a href="https://creativecommons.org/licenses/by/4.0/deed.zh" rel="external nofollow noreferrer" target="_blank">CC BY 4.0</a>
                    许可协议。转载请注明来源
                    <a href="/dai_modest/about" target="_blank">戴某人</a>
                    !
                </span>
            </div>
        
    </div>

    <script async defer>
      document.addEventListener("copy", function (e) {
        let toastHTML = '<span>复制成功，请遵循本文的转载规则</span><button class="btn-flat toast-action" onclick="navToReprintStatement()" style="font-size: smaller">查看</a>';
        M.toast({html: toastHTML})
      });

      function navToReprintStatement() {
        $("html, body").animate({scrollTop: $("#reprint-statement").offset().top - 80}, 800);
      }
    </script>



            <div class="tag_share" style="display: block;">
                <div class="post-meta__tag-list" style="display: inline-block;">
                    
                        <div class="article-tag">
                            
                                <a href="/dai_modest/tags/java/">
                                    <span class="chip bg-color">java</span>
                                </a>
                            
                        </div>
                    
                </div>
                <div class="post_share" style="zoom: 80%; width: fit-content; display: inline-block; float: right; margin: -0.15rem 0;">
                    <link rel="stylesheet" type="text/css" href="/dai_modest/libs/share/css/share.min.css">
<div id="article-share">

    
    <div class="social-share" data-sites="twitter,facebook,google,qq,qzone,wechat,weibo,douban,linkedin" data-wechat-qrcode-helper="<p>微信扫一扫即可分享！</p>"></div>
    <script src="/dai_modest/libs/share/js/social-share.min.js"></script>
    

    
    <script type="text/javascript" src="//s7.addthis.com/js/300/addthis_widget.js#pubid="></script>
    <div class="addthis_inline_share_toolbox"></div>
    

</div>

                </div>
            </div>
            
                <style>
    #reward {
        margin: 40px 0;
        text-align: center;
    }

    #reward .reward-link {
        font-size: 1.4rem;
        line-height: 38px;
    }

    #reward .btn-floating:hover {
        box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2), 0 5px 15px rgba(0, 0, 0, 0.2);
    }

    #rewardModal {
        width: 320px;
        height: 350px;
    }

    #rewardModal .reward-title {
        margin: 15px auto;
        padding-bottom: 5px;
    }

    #rewardModal .modal-content {
        padding: 10px;
    }

    #rewardModal .close {
        position: absolute;
        right: 15px;
        top: 15px;
        color: rgba(0, 0, 0, 0.5);
        font-size: 1.3rem;
        line-height: 20px;
        cursor: pointer;
    }

    #rewardModal .close:hover {
        color: #ef5350;
        transform: scale(1.3);
        -moz-transform:scale(1.3);
        -webkit-transform:scale(1.3);
        -o-transform:scale(1.3);
    }

    #rewardModal .reward-tabs {
        margin: 0 auto;
        width: 210px;
    }

    .reward-tabs .tabs {
        height: 38px;
        margin: 10px auto;
        padding-left: 0;
    }

    .reward-content ul {
        padding-left: 0 !important;
    }

    .reward-tabs .tabs .tab {
        height: 38px;
        line-height: 38px;
    }

    .reward-tabs .tab a {
        color: #fff;
        background-color: #ccc;
    }

    .reward-tabs .tab a:hover {
        background-color: #ccc;
        color: #fff;
    }

    .reward-tabs .wechat-tab .active {
        color: #fff !important;
        background-color: #22AB38 !important;
    }

    .reward-tabs .alipay-tab .active {
        color: #fff !important;
        background-color: #019FE8 !important;
    }

    .reward-tabs .reward-img {
        width: 210px;
        height: 210px;
    }
</style>

<div id="reward">
    <a href="#rewardModal" class="reward-link modal-trigger btn-floating btn-medium waves-effect waves-light red">赏</a>

    <!-- Modal Structure -->
    <div id="rewardModal" class="modal">
        <div class="modal-content">
            <a class="close modal-close"><i class="fas fa-times"></i></a>
            <h4 class="reward-title">你的赏识是我前进的动力</h4>
            <div class="reward-content">
                <div class="reward-tabs">
                    <ul class="tabs row">
                        <li class="tab col s6 alipay-tab waves-effect waves-light"><a href="#alipay">支付宝</a></li>
                        <li class="tab col s6 wechat-tab waves-effect waves-light"><a href="#wechat">微 信</a></li>
                    </ul>
                    <div id="alipay">
                        <img src="/dai_modest/medias/reward/alipay.jpg" class="reward-img" alt="支付宝打赏二维码">
                    </div>
                    <div id="wechat">
                        <img src="/dai_modest/medias/reward/wechat.png" class="reward-img" alt="微信打赏二维码">
                    </div>
                </div>
            </div>
        </div>
    </div>
</div>

<script>
    $(function () {
        $('.tabs').tabs();
    });
</script>

            
        </div>
    </div>

    

    

    

    

    

    

    

    

    

<article id="prenext-posts" class="prev-next articles">
    <div class="row article-row">
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge left-badge text-color">
                <i class="fas fa-chevron-left"></i>&nbsp;上一篇</div>
            <div class="card">
                <a href="/dai_modest/2022/04/16/java-bing-fa-bian-cheng-de-yi-zhu-di-wu-zhang-zong-jie/">
                    <div class="card-image">
                        
                        
                        <img src="/dai_modest/medias/featureimages/6.jpg" class="responsive-img" alt="《java并发编程的艺术》第五章总结">
                        
                        <span class="card-title">《java并发编程的艺术》第五章总结</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            Lock接口，队列同步器，重入锁，读写锁，condition接口
                        
                    </div>
                    <div class="publish-info">
                        <span class="publish-date">
                            <i class="far fa-clock fa-fw icon-date"></i>2022-04-16
                        </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/" class="post-category">
                                    书籍
                                </a>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/" class="post-category">
                                    笔记类
                                </a>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/%E3%80%8Ajava%E5%B9%B6%E5%8F%91%E7%BC%96%E7%A8%8B%E7%9A%84%E8%89%BA%E6%9C%AF%E3%80%8B/" class="post-category">
                                    《java并发编程的艺术》
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/dai_modest/tags/java/">
                        <span class="chip bg-color">java</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
        
        <div class="article col s12 m6" data-aos="fade-up">
            <div class="article-badge right-badge text-color">
                下一篇&nbsp;<i class="fas fa-chevron-right"></i>
            </div>
            <div class="card">
                <a href="/dai_modest/2022/04/16/java-bing-fa-bian-cheng-de-yi-zhu-di-liu-zhang-zong-jie-2/">
                    <div class="card-image">
                        
                        
                        <img src="/dai_modest/medias/featureimages/9.jpg" class="responsive-img" alt="《java并发编程的艺术》第六章总结2">
                        
                        <span class="card-title">《java并发编程的艺术》第六章总结2</span>
                    </div>
                </a>
                <div class="card-content article-content">
                    <div class="summary block-with-text">
                        
                            java阻塞队列，Fork/Join框架
                        
                    </div>
                    <div class="publish-info">
                            <span class="publish-date">
                                <i class="far fa-clock fa-fw icon-date"></i>2022-04-16
                            </span>
                        <span class="publish-author">
                            
                            <i class="fas fa-bookmark fa-fw icon-category"></i>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/" class="post-category">
                                    书籍
                                </a>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/" class="post-category">
                                    笔记类
                                </a>
                            
                            <a href="/dai_modest/categories/%E4%B9%A6%E7%B1%8D/%E7%AC%94%E8%AE%B0%E7%B1%BB/%E3%80%8Ajava%E5%B9%B6%E5%8F%91%E7%BC%96%E7%A8%8B%E7%9A%84%E8%89%BA%E6%9C%AF%E3%80%8B/" class="post-category">
                                    《java并发编程的艺术》
                                </a>
                            
                            
                        </span>
                    </div>
                </div>
                
                <div class="card-action article-tags">
                    
                    <a href="/dai_modest/tags/java/">
                        <span class="chip bg-color">java</span>
                    </a>
                    
                </div>
                
            </div>
        </div>
        
    </div>
</article>

</div>


<script>
    $('#articleContent').on('copy', function (e) {
        // IE8 or earlier browser is 'undefined'
        if (typeof window.getSelection === 'undefined') return;

        var selection = window.getSelection();
        // if the selection is short let's not annoy our users.
        if (('' + selection).length < Number.parseInt('120')) {
            return;
        }

        // create a div outside of the visible area and fill it with the selected text.
        var bodyElement = document.getElementsByTagName('body')[0];
        var newdiv = document.createElement('div');
        newdiv.style.position = 'absolute';
        newdiv.style.left = '-99999px';
        bodyElement.appendChild(newdiv);
        newdiv.appendChild(selection.getRangeAt(0).cloneContents());

        // we need a <pre> tag workaround.
        // otherwise the text inside "pre" loses all the line breaks!
        if (selection.getRangeAt(0).commonAncestorContainer.nodeName === 'PRE' || selection.getRangeAt(0).commonAncestorContainer.nodeName === 'CODE') {
            newdiv.innerHTML = "<pre>" + newdiv.innerHTML + "</pre>";
        }

        var url = document.location.href;
        newdiv.innerHTML += '<br />'
            + '来源: 戴某的博客<br />'
            + '文章作者: 戴某人<br />'
            + '文章链接: <a href="' + url + '">' + url + '</a><br />'
            + '本文章著作权归作者：戴某人所有，任何形式的转载都请注明出处。';

        selection.selectAllChildren(newdiv);
        window.setTimeout(function () {bodyElement.removeChild(newdiv);}, 200);
    });
</script>


<!-- 代码块功能依赖 -->
<script type="text/javascript" src="/dai_modest/libs/codeBlock/codeBlockFuction.js"></script>

<!-- 代码语言 -->

<script type="text/javascript" src="/dai_modest/libs/codeBlock/codeLang.js"></script>


<!-- 代码块复制 -->

<script type="text/javascript" src="/dai_modest/libs/codeBlock/codeCopy.js"></script>


<!-- 代码块收缩 -->

<script type="text/javascript" src="/dai_modest/libs/codeBlock/codeShrink.js"></script>


    </div>
    <div id="toc-aside" class="expanded col l3 hide-on-med-and-down">
        <div class="toc-widget card" style="background-color: white;">
            <div class="toc-title"><i class="far fa-list-alt"></i>&nbsp;&nbsp;目录</div>
            <div id="toc-content"></div>
        </div>
    </div>
</div>

<!-- TOC 悬浮按钮. -->

<div id="floating-toc-btn" class="hide-on-med-and-down">
    <a class="btn-floating btn-large bg-color">
        <i class="fas fa-list-ul"></i>
    </a>
</div>


<script src="/dai_modest/libs/tocbot/tocbot.min.js"></script>
<script>
    $(function () {
        tocbot.init({
            tocSelector: '#toc-content',
            contentSelector: '#articleContent',
            headingsOffset: -($(window).height() * 0.4 - 45),
            collapseDepth: Number('0'),
            headingSelector: 'h2, h3, h4'
        });

        // modify the toc link href to support Chinese.
        let i = 0;
        let tocHeading = 'toc-heading-';
        $('#toc-content a').each(function () {
            $(this).attr('href', '#' + tocHeading + (++i));
        });

        // modify the heading title id to support Chinese.
        i = 0;
        $('#articleContent').children('h2, h3, h4').each(function () {
            $(this).attr('id', tocHeading + (++i));
        });

        // Set scroll toc fixed.
        let tocHeight = parseInt($(window).height() * 0.4 - 64);
        let $tocWidget = $('.toc-widget');
        $(window).scroll(function () {
            let scroll = $(window).scrollTop();
            /* add post toc fixed. */
            if (scroll > tocHeight) {
                $tocWidget.addClass('toc-fixed');
            } else {
                $tocWidget.removeClass('toc-fixed');
            }
        });

        
        /* 修复文章卡片 div 的宽度. */
        let fixPostCardWidth = function (srcId, targetId) {
            let srcDiv = $('#' + srcId);
            if (srcDiv.length === 0) {
                return;
            }

            let w = srcDiv.width();
            if (w >= 450) {
                w = w + 21;
            } else if (w >= 350 && w < 450) {
                w = w + 18;
            } else if (w >= 300 && w < 350) {
                w = w + 16;
            } else {
                w = w + 14;
            }
            $('#' + targetId).width(w);
        };

        // 切换TOC目录展开收缩的相关操作.
        const expandedClass = 'expanded';
        let $tocAside = $('#toc-aside');
        let $mainContent = $('#main-content');
        $('#floating-toc-btn .btn-floating').click(function () {
            if ($tocAside.hasClass(expandedClass)) {
                $tocAside.removeClass(expandedClass).hide();
                $mainContent.removeClass('l9');
            } else {
                $tocAside.addClass(expandedClass).show();
                $mainContent.addClass('l9');
            }
            fixPostCardWidth('artDetail', 'prenext-posts');
        });
        
    });
</script>

    

</main>




    <footer class="page-footer bg-color">
    
        <link rel="stylesheet" href="/dai_modest/libs/aplayer/APlayer.min.css">
<style>
    .aplayer .aplayer-lrc p {
        
        display: none;
        
        font-size: 12px;
        font-weight: 700;
        line-height: 16px !important;
    }

    .aplayer .aplayer-lrc p.aplayer-lrc-current {
        
        display: none;
        
        font-size: 15px;
        color: #42b983;
    }

    
    .aplayer.aplayer-fixed.aplayer-narrow .aplayer-body {
        left: -66px !important;
    }

    .aplayer.aplayer-fixed.aplayer-narrow .aplayer-body:hover {
        left: 0px !important;
    }

    
</style>
<div class="">
    
    <div class="row">
        <meting-js class="col l8 offset-l2 m10 offset-m1 s12"
                   server="netease"
                   type="playlist"
                   id="503838841"
                   fixed='true'
                   autoplay='false'
                   theme='#42b983'
                   loop='all'
                   order='random'
                   preload='auto'
                   volume='0.7'
                   list-folded='true'
        >
        </meting-js>
    </div>
</div>

<script src="/dai_modest/libs/aplayer/APlayer.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/meting@2/dist/Meting.min.js"></script>

    

    <div class="container row center-align"
         style="margin-bottom: 0px !important;">
        <div class="col s12 m8 l8 copy-right">
            Copyright&nbsp;&copy;
            
                <span id="year">2019-2023</span>
            
            <span id="year">2019</span>
            <a href="/dai_modest/about" target="_blank">戴某人</a>
            |&nbsp;Powered by&nbsp;<a href="https://hexo.io/" target="_blank">Hexo</a>
            |&nbsp;Theme&nbsp;<a href="https://github.com/blinkfox/hexo-theme-matery" target="_blank">Matery</a>
            <br>
            
                &nbsp;<i class="fas fa-chart-area"></i>&nbsp;站点总字数:&nbsp;<span
                        class="white-color">128.1k</span>
            
            
            
                
            
            
                <span id="busuanzi_container_site_pv">
                &nbsp;|&nbsp;<i class="far fa-eye"></i>&nbsp;总访问量:&nbsp;
                    <span id="busuanzi_value_site_pv" class="white-color"></span>
            </span>
            
            
                <span id="busuanzi_container_site_uv">
                &nbsp;|&nbsp;<i class="fas fa-users"></i>&nbsp;总访问人数:&nbsp;
                    <span id="busuanzi_value_site_uv" class="white-color"></span>
            </span>
            
            <br>

            <!-- 运行天数提醒. -->
            
            <br>
            
        </div>
        <div class="col s12 m4 l4 social-link social-statis">


    <a href="mailto:861796830@qq.com" class="tooltipped" target="_blank" data-tooltip="邮件联系我" data-position="top" data-delay="50">
        <i class="fas fa-envelope-open"></i>
    </a>







    <a href="tencent://AddContact/?fromId=50&fromSubId=1&subcmd=all&uin=861796830" class="tooltipped" target="_blank" data-tooltip="QQ联系我: 861796830" data-position="top" data-delay="50">
        <i class="fab fa-qq"></i>
    </a>







    <a href="/dai_modest/atom.xml" class="tooltipped" target="_blank" data-tooltip="RSS 订阅" data-position="top" data-delay="50">
        <i class="fas fa-rss"></i>
    </a>

</div>
    </div>
</footer>

<div class="progress-bar"></div>


    <!-- 搜索遮罩框 -->
<div id="searchModal" class="modal">
    <div class="modal-content">
        <div class="search-header">
            <span class="title"><i class="fas fa-search"></i>&nbsp;&nbsp;搜索</span>
            <input type="search" id="searchInput" name="s" placeholder="请输入搜索的关键字"
                   class="search-input">
        </div>
        <div id="searchResult"></div>
    </div>
</div>

<script type="text/javascript">
$(function () {
    var searchFunc = function (path, search_id, content_id) {
        'use strict';
        $.ajax({
            url: path,
            dataType: "xml",
            success: function (xmlResponse) {
                // get the contents from search data
                var datas = $("entry", xmlResponse).map(function () {
                    return {
                        title: $("title", this).text(),
                        content: $("content", this).text(),
                        url: $("url", this).text()
                    };
                }).get();
                var $input = document.getElementById(search_id);
                var $resultContent = document.getElementById(content_id);
                $input.addEventListener('input', function () {
                    var str = '<ul class=\"search-result-list\">';
                    var keywords = this.value.trim().toLowerCase().split(/[\s\-]+/);
                    $resultContent.innerHTML = "";
                    if (this.value.trim().length <= 0) {
                        return;
                    }
                    // perform local searching
                    datas.forEach(function (data) {
                        var isMatch = true;
                        var data_title = data.title.trim().toLowerCase();
                        var data_content = data.content.trim().replace(/<[^>]+>/g, "").toLowerCase();
                        var data_url = data.url;
                        data_url = data_url.indexOf('/') === 0 ? data.url : '/' + data_url;
                        var index_title = -1;
                        var index_content = -1;
                        var first_occur = -1;
                        // only match artiles with not empty titles and contents
                        if (data_title !== '' && data_content !== '') {
                            keywords.forEach(function (keyword, i) {
                                index_title = data_title.indexOf(keyword);
                                index_content = data_content.indexOf(keyword);
                                if (index_title < 0 && index_content < 0) {
                                    isMatch = false;
                                } else {
                                    if (index_content < 0) {
                                        index_content = 0;
                                    }
                                    if (i === 0) {
                                        first_occur = index_content;
                                    }
                                }
                            });
                        }
                        // show search results
                        if (isMatch) {
                            str += "<li><a href='" + data_url + "' class='search-result-title'>" + data_title + "</a>";
                            var content = data.content.trim().replace(/<[^>]+>/g, "");
                            if (first_occur >= 0) {
                                // cut out 100 characters
                                var start = first_occur - 20;
                                var end = first_occur + 80;
                                if (start < 0) {
                                    start = 0;
                                }
                                if (start === 0) {
                                    end = 100;
                                }
                                if (end > content.length) {
                                    end = content.length;
                                }
                                var match_content = content.substr(start, end);
                                // highlight all keywords
                                keywords.forEach(function (keyword) {
                                    var regS = new RegExp(keyword, "gi");
                                    match_content = match_content.replace(regS, "<em class=\"search-keyword\">" + keyword + "</em>");
                                });

                                str += "<p class=\"search-result\">" + match_content + "...</p>"
                            }
                            str += "</li>";
                        }
                    });
                    str += "</ul>";
                    $resultContent.innerHTML = str;
                });
            }
        });
    };

    searchFunc('/dai_modest/search.xml', 'searchInput', 'searchResult');
});
</script>

    <!-- 回到顶部按钮 -->
<div id="backTop" class="top-scroll">
    <a class="btn-floating btn-large waves-effect waves-light" href="#!">
        <i class="fas fa-arrow-up"></i>
    </a>
</div>


    <script src="/dai_modest/libs/materialize/materialize.min.js"></script>
    <script src="/dai_modest/libs/masonry/masonry.pkgd.min.js"></script>
    <script src="/dai_modest/libs/aos/aos.js"></script>
    <script src="/dai_modest/libs/scrollprogress/scrollProgress.min.js"></script>
    <script src="/dai_modest/libs/lightGallery/js/lightgallery-all.min.js"></script>
    <script src="/dai_modest/js/matery.js"></script>

    <!-- Baidu Analytics -->

    <!-- Baidu Push -->

<script>
    (function () {
        var bp = document.createElement('script');
        var curProtocol = window.location.protocol.split(':')[0];
        if (curProtocol === 'https') {
            bp.src = 'https://zz.bdstatic.com/linksubmit/push.js';
        } else {
            bp.src = 'http://push.zhanzhang.baidu.com/push.js';
        }
        var s = document.getElementsByTagName("script")[0];
        s.parentNode.insertBefore(bp, s);
    })();
</script>

    
    <script src="/dai_modest/libs/others/clicklove.js" async="async"></script>
    
    
    <script async src="/dai_modest/libs/others/busuanzi.pure.mini.js"></script>
    

    

    

    <!--腾讯兔小巢-->
    
        <div style="position:fixed;bottom:125px;right:16px;cursor: pointer;">
            <a title="兔小巢" target="_blank" rel="noopener" href="https://support.qq.com/products/"><i class="fa fa-comments fa-3x"  aria-hidden="true"></i></a>
        </div>
    
    
    <script type="text/javascript" color="0,0,255"
        pointColor="0,0,255" opacity='0.7'
        zIndex="-1" count="99"
        src="/dai_modest/libs/background/canvas-nest.js"></script>
    

    
    
    <script type="text/javascript" size="150" alpha='0.6'
        zIndex="-1" src="/dai_modest/libs/background/ribbon.min.js" async="async"></script>
    

    
    <script type="text/javascript" src="/dai_modest/libs/background/ribbon-dynamic.js" async="async"></script>
    

    
    <script src="/dai_modest/libs/instantpage/instantpage.js" type="module"></script>
    

<script src="/dai_modest/live2dw/lib/L2Dwidget.min.js?094cbace49a39548bed64abff5988b05"></script><script>L2Dwidget.init({"log":false,"pluginJsPath":"lib/","pluginModelPath":"assets/","pluginRootPath":"live2dw/","tagMode":false});</script></body>

</html>
